In order to be useful for molding and other industrial purposes, rigid plastics such as polyvinyl chloride are generally reinforced with particles of rubbery polymers, such as polybutadiene, polyacrylates, copolymers of butadiene and styrene, etc. The addition of rubbery polymers to polyvinyl chloride improves its impact strength, i.e. the ability to withstand a rapidly applied shock. However, the addition of such rubbery materials often adversely affects physical properties such as tensile strength, clarity, heat distortion temperature, hardness, aging stability, color fastness, etc. Furthermore, the addition of larger amounts of rubbery materials, which would produce a product of maximum impact strength would result in a modified polyvinyl chloride which is too soft for many uses. In commercial practice, the modified polyvinyl chlorides represent a compromise between the desire to increase the impact strength and the maintenance of other required physical properties.
Among the rubbery materials commonly in use to modify polyvinyl chloride are polybutadiene and copolymers of styrene and butadiene. Because of processing difficulties, pure polybutadiene can be used in only relatively small amounts, and the small amounts have generally not been sufficient to provide the desired improvement in impact strength. SBR* has shown some effectiveness, the particular properties of SBR-modified polyvinyl chloride depending in large measure upon the relative amounts of styrene and butadiene, but these also have presented processing difficulties and have detracted from the other desired physical properties of polyvinyl chloride. In particular, the incorporation of significant amounts of SBR into polyvinyl chloride has resulted in significantly lower heat stability and weatherability. Notwithstanding these drawbacks polybutadiene and SBR have been used because of their availability and low cost. FNT *styrene/butadiene rubber
To overcome the difficulty of incorporating polybutadiene into polyvinyl chloride, the use of styrene and/or methylmethacrylate grafted on SBR-butyl acrylate or SBR resins has been proposed in U.S. Pat. Nos. 3,644,249 and 3,657,390. However grafted side chains, intermittently distributed along the elastomer polymer backbone lack the degree of efficiency desired. In the graft polymer, individual segments e.g. polybutadiene segments, are subject to attack by solvents and are sensitive to light. The final finishing step in forming the polymers disclosed in U.S. Pat. No. 3,644,249 is grafting with polystyrene which is not compatible with polyvinyl chloride but which rises to the surface of the polymer particles to improve gloss.
Accordingly, it is a principal object of this invention to provide a modified polymeric composition, based on butadiene or SBR, which, when mixed with a polyvinyl chloride resin composition, would yield a product with enhanced impact strength and compatibility.
Another object of this invention is to provide efficient use of methylmethacrylate in obviating incompatibility of polybutadiene in polyvinyl chloride when incorporation of these polymers is desired.
Another object of this invention is to obtain a polyvinyl chloride composition with enhanced impact strength, but without the deterioration in physical properties which have heretofore resulted from the use of polybutadiene or SBR.
Yet another object of this invention is to develop a modifier for polyvinyl chloride which can be in a form (for example, powder or flakes) which can be easily blended into a polyvinyl chloride resin.